In case of power failure, emergency lighting should produce mostly locally limited light for a limited period of time in order, for example, to help people get oriented and to make it possible to initiate certain measures. By “power grid” we mean here primarily alternating-voltage power grids with, for example, 230 V, but also direct-voltage power grids with voltages of, for example, 24 or 48 V.
Emergency lighting is often prescribed by law in industry and in the public sector. In that connection, one primarily employs storage batteries for the purpose of power grid buffering, for example, for fluorescent lamps at emergency exits. In this connection, it must be noted that the use of storage batteries is relatively expensive and frequently requires maintenance, so that emergency lighting is often dispensed with, provided it is not prescribed by law.